Headset and other telephonic device designs used for telephony must deal with the acoustic response from device speakers being detected by the device microphone and then sent back to the far-end speaker, which after the delays inherent in any telecommunications circuit may be detected by the far-end user as an echo of their own voice. Here, the “transmit signal” refers to the audio signal from a near end user, e.g. a headset wearer, transmitted to a far-end listener. The “receive signal” refers to the audio signal received by the headset wearer from the far-end talker. In the prior art, one solution to this echo problem was to ensure the acoustic isolation from the headset speaker to the headset microphone is so great as to render any residual echo as imperceptible. For example, one solution is to use a headset with a long boom to place the microphone near the user's mouth.
However, such a headset may be uncomfortable to wear or too restrictive in certain environments. Furthermore, many applications require a headset design that cannot achieve the acoustic isolation required, such as a headset with a very short microphone boom used in either cellular telephony or Voice over Internet Protocol (VoIP), or more generally Voice over Packet (VoP) applications. In these applications, the delay through the telecommunications network can be hundreds of milliseconds, which can make even a small amount of acoustic echo annoying to the far-end user. The required acoustic isolation is more difficult to achieve with boomless headsets, hands-free headsets, speaker-phones, and other devices in which a microphone and speaker may be in close proximity. One solution described in the prior art has been to utilize an echo cancellation technique to reduce the acoustic echo. Such techniques are discussed for example, in U.S. Pat. No. 6,415,029 entitled “Echo Canceler and Double-Talk Detector for Use in a Communications Unit.” However, such techniques focus on the voice signal alone as opposed to acoustic echo in the noise sources, thereby limiting their effectiveness.
Headset and other telephonic device designs must also deal with background noise, caused by a variety of noise sources in the headset wearer's vicinity, such as other people conversing nearby, wind noise in an automobile, machinery & ventilation noise, loud music and intercom announcements in public places. These sources may either be diffuse or point noise sources. In the prior art, such acoustic interference is normally managed by the use of a long microphone boom, which places the microphone as close as possible to the user's mouth, a voice tube, which has the same effect as a long boom, or a noise canceling microphone, which enhances the microphone response in one direction oriented towards the user's mouth and attenuates the response from the other directions. However, for many applications these solutions are either inadequate, such as very high noise environments, or are not compatible with the stylistic and user comfort requirements on the headset, such as a headset with a short microphone boom. Also, when using noise-canceling microphones, if the microphone is not properly positioned—as is often the case—the noise reducing mechanism is rendered useless. In these cases, additional background noise reduction is required in the microphone output signal.
Thus, there has been a need for improvements in the reduction of acoustic echo and reduction of background noise. More specifically, there has been a need for improved systems and methods for echo cancellation and noise reduction techniques.